The function of excitable tissues such as the heart, critically depends on a delicate balance of ion movements through the cell membrane. Defects of the pathways of ion permeability lead to loss of function which may often be restored by drugs that act upon these. The objective of the present research program is to elucidate, at the molecular level, the mechanisms by which ions move through heart cell membranes and to explore the ways in which these ion movements can be affected by pharmacological agents. Efforts will be made to select preparations of cardiac origin through the membranes of which ion movement can be studied with quantitative accuracy using three different techniques: macroscopic (voltage clamp), fluctuation (noise) and microscopic (single channel) recording of ionic currents. Simultaneous use of these techniques is considered to be a unique feature required in order to ascertain that the macroscopic physiological responses are indeed a manifestation of the unitary single channel events under study. Channel whose properties are most appropriately resolved by macroscopic, fluctuation and microscopic techniques will be identified. They will be studied at a level of molecular detail previously developed in our laboratory for the gramicidin A model system. Specifically, attempts will be made to identify spontaneous changes in channel permeability and/or ion selectivity, to locate the major rate-limiting steps for ion movement, and to assess the role of charged and/or dipolar residues at the mouth or within the channel. The physiochemical properties (fluidity, surface charge, surface dipoles, membrane asymmetry) of the bilayer portion of the cell membrane will be studied by the use of ionic probes developed extensively in this laboratory. A combined study of ion channels and of the supporting lipid bilayer provides a unique system in which one can uncover functionally significant interactions between the channel protein and its lipid environment. It also provides a unique opportunity to elucidate the basic mechanisms by which pharmacological agents, for example anaesthetics and channel blockers, operate at the molecular level.